[Edit 2: Solved]
Was not an issue with agetty it was graphics related. The login prompt was actually there (i.e. typing i could type in my username, hit enter and below that the Password prompt would start showing up. From there all console text was fine. Have no idea what's causing it but isn't a showstopper.

[Edit 1: changed title since I've finally found useful messages against agetty]

I have a system with two gentoo installs. There is a working install that I am having no trouble with, however there is a new install on new hard drives that I am trying to get up and running. The major difference between the systems is switching away from systemd back to openrc.

Of note, there are two AMD RX 570 cards in this system. Also of note I have a custom initramfs with init that launches into openrc. This init simply runs btrfs device scan, mounts / switches root, then passes to openrc-init (or systemd for the working install--I had to build a new initramfs for the openrc one). The initramfs is necessary because the working install is raid 1 across two drives, the new install is raid10 across 4 drives, no modules are loaded.

On booting the new install init launches and services are starting (I can't see any failing services but it's moving fast). After the local service starts [Ok] there is nothing else that gets printed to screen. Xorg and KDE are installed, however are NOT enabled right now.

The amdgpu driver is a module not compiled in. I have installed sys-kernel/linux-firmware-20181218 and sys-kernel/linux-headers-4.1.

Copied .config from old to new, ran make oldconfig, only config change between two kernels was enabling openrc support, anything else new = N:
Gentoo Linux ---> Support for init systems, system and service managers --->

Code:

[b][*] OpenRC, runit and other script based systems and managers[/b]
[*] systemd

Note that for the new install, changing video=HDMI-B-1:1280x720@60 to video=HDMI-B-1 results in an all black screen, no cursor.
OpenRC is NOT set to PARALLEL start and no services that would typically block are enabled.

Since /dev is a pseudofilesystem, checking it from outside may not show you the state it has when the bad system is running. I use openrc and do not have a /dev/agetty node at all. My installed /sbin/agetty does not use such a node. My inittab is functionally equivalent to yours. (I have more agetty instances enabled, but for the ones we both enabled, mine look like yours, aside from my use of --noclear.) According to your logs, yours wants to use that node, and cannot find it. To be sure we are working the same problem, your current objective is to get the openrc-based system to bring up a text console with a working agetty, so that local users can log in, correct? We are not yet debugging anything Xorg related, since you have that set not to autostart.

When the problem manifests, your monitor does not show the agetty prompt. Does it show a text cursor at all? Is it in powersave mode (as would happen if you turned off the computer and left the monitor on), showing a blank screen with no content (backlight enabled, but every pixel painted black, as some screen-blanking software will do prior to powering down the monitor), or a blank screen with just a text input cursor?

Do you have a separate working computer that you could use to try to ssh into the broken system, so that you can explore it while it is up? A Windows system, Linux system, Mac, or even a smartphone with the right app can be used for this purpose.